Photosynthetic temperature responses of Eucalyptus globulus and Eucalyptus nitens

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Abstract
Steady-state photosynthetic responses to leaf temperature of 4-year-old Eucalyptus globulus Labill. and E. nitens (Deane and Maiden) Maiden trees were measured between 10 and 35 °C at approximately monthly intervals from early spring to midwinter. The photosynthetic temperature optimum of recently expanded leaves in the sun canopy was linearly related to the average temperature of the preceding week during the 9-month measurement period. The optimum temperature for net photosynthesis of E. globulus increased from 17 to 23 °C as the mean daily temperature increased from 7 to 16 °C. Similarly, the optimum temperature for net photosynthesis of E. nitens increased from 14 to 20 °C as the mean daily temperature increased from 7 to 19 °C. The temperature for maximum photosynthetic response of E. globulus and E. nitens was similar at each measurement time, but the photosynthetic performance of E. nitens was less sensitive to temperatures above and below this optimum than that of E. globulus. In December, the apical shoots of branches of E. globulus had a net photosynthetic temperature optimum of between 10 and 15 °C. The corresponding values for expanding leaves, fully expanded leaves from the current year's growth, and fully expanded leaves from the previous year's growth were 15, 20 and 20–25 °C, respectively.

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